In the manufacture of granular materials such as cement it is conventional to introduce comminuted particulate material to a sifter or separator having a separating zone in which the particulate material is reduced to relatively fine and relatively coarse particles. A gas stream flows through the separating zone at such velocity as to entrain relatively fine particles and convey them downstream of the separating zone for storage or further processing. The coarse particles which are not entrained in the gas stream are discharged from the separating zone for further comminution or other treatment. The fine particles which are entrained in the gas stream conventionally are separated from the gas downstream of the separating zone.
The separation of the gas and fine particles conventionally occurs in a cyclone separator in which the gas and the particles flow out of the separator along different paths. The efficiency of such separators depends in large part upon the volume and rate of flow of the gas. Any reduction in the volume of such gas could affect adversely the separation of the particles from the gas.
The treatment to which the relatively fine particles downstream of the separating zone may be subjected depends in large measure on the size or fineness of the relatively fine particles entrained by the gas stream. The fineness of such particles may be regulated by the volume and velocity of the gas stream that passes through the separating zone. However, and as is indicated above, changes in the volume and velocity of the gas stream affect the efficiency of the gas/fine particle separation. Reductions in the efficiency of the gas/fine particle separation can have adverse consequences on the further treatment of the particles downstream of such separation.
In some instances the gas stream that is introduced to the separating zone may be heated for the purpose of drying or preheating the particles. In other instances, the gas may be cooled for the purpose of cooling the particles. In either instance a reduction in the volume of air which is used to transport entrained fine particles to the gas/fine particle separator may have adverse consequences on the dryness or temperature of the fine particles.
A principal object of the invention is to provide apparatus and methods which overcome the undesirable effects referred to above.